Split optical front end receivers

ABSTRACT

An optical receiver with improved dynamic range may include at least one directional coupler having at least one input configured to couple to an optical fiber. The optical receiver may include a first signal path including a first photodetector coupled to an output of the at least one directional coupler, a first transimpedance amplifier (TIA) including an input coupled to the first photodetector, and an adder coupled to an output of the first TIA. The optical receiver may include a second signal path including a second photodetector coupled to an output of the at least one directional coupler, a second TIA including an input coupled to the second photodetector, and the adder coupled to an output of the second TIA. Further, the optical receiver may include an optical power sensing circuit coupled to at least one of the first TIA, the second TIA, and the adder.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalApp. No. 62/570,765, filed Oct. 11, 2017, and U.S. Provisional App. No.62/652,633, filed Apr. 4, 2018. The 62/570,765 application and the62/652,633 application are incorporated herein by reference.

FIELD

The embodiments discussed herein relate to split optical front endreceivers.

BACKGROUND

Unless otherwise indicated herein, the materials described herein arenot prior art to the claims in the present application and are notadmitted to be prior art by inclusion in this section.

Fiber optics and optoelectronics are important aspects of modern opticalnetworks because they allow for efficient and accurate transmission ofoptical data between various components in a network system. An opticaltransceiver module (“transceiver”), which may include an opticalreceiver, is an example of a modular component that is used in opticalnetworks.

The subject matter claimed herein is not limited to implementations thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one example technology area where some implementationsdescribed herein may be practiced.

SUMMARY

Some embodiments discussed herein are related to split optical front endreceivers.

In an example embodiment, an optical receiver system includes an opticalreceiver that includes a directional coupler, a first signal path, asecond signal path, and an optical power sensing circuit. Thedirectional coupler may be configured to receive an optical signal andsplit the optical signal into a first signal including a first portionof the optical signal and a second signal including a second portion ofthe optical signal. The first signal path may be configured to receivethe first signal and may include a first photodetector, a firsttransimpedance amplifier (TIA), and an interpolator. The first TIA maybe coupled to the first photodetector. The interpolator may be coupledto the first TIA. The second signal path may be configured to receivethe second signal and may include a second photodetector, a second TIA,and the interpolator. The second TIA may be coupled to the secondphotodetector. The interpolator may be coupled to the second TIA. Theinterpolator may be configured to generate an output signal based on atleast one of an output of the first TIA and an output of the second TIA.The optical power sensing circuit may be configured to detect a powerlevel of at least one of a signal within the first signal path, a signalwithin the second signal path, or the output signal from theinterpolator. The optical receiver may be configured to select at leastone of the first signal path or the second signal path to generate theoutput signal based on the detected power level.

In another example embodiment, an optical receiver includes at least onedirectional coupler, a first signal path, a second signal path, and anoptical power sensing circuit. At least one input of the directionalcoupler may be configured to couple to an optical fiber. The firstsignal path may include a first photodetector coupled to an output ofthe at least one directional coupler, a first TIA including an inputcoupled to the first photodetector, and an adder coupled to an output ofthe first TIA. The second signal path may include a second photodetectorcoupled to an output of the at least one directional coupler, a secondTIA including an input coupled to the second photodetector, and theadder coupled to an output of the second TIA. The optical power sensingcircuit may be coupled to at least one of the first TIA, the second TIA,the adder, and an output of the optical receiver.

In another example embodiment, a method may include splitting an opticalsignal into a first optical signal and a second optical signal via adirectional coupler, the first optical signal including a first portionof the optical signal and the second optical signal including a second,lesser portion of the optical signal. The method may also includeconverting the first optical signal into a first current signal in afirst signal path. The method may also include converting the secondoptical signal into a second current signal in a second signal path. Themethod may also include amplifying the first current signal to generatea first amplified signal in the first signal path. The method may alsoinclude directly or indirectly detecting a power level of the opticalsignal. The method may also include disabling the first signal path andenabling the second signal path in response to the power level of theoptical signal increasing above a threshold value.

Additional features and advantages of the disclosure will be set forthin the description which follows, and in part will be obvious from thedescription, or may be learned by the practice of the disclosure. Thefeatures and advantages of the disclosure may be realized and obtainedby means of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present disclosurewill become more fully apparent from the following description andappended claims, or may be learned by the practice of the disclosure asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent disclosure, a more particular description of the disclosure willbe rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the disclosure and aretherefore not to be considered limiting of its scope. The disclosurewill be described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 illustrates an example optical receiver system including aphotonic integrated circuit;

FIG. 2A depicts an example optical receiver system;

FIG. 2B depicts another example optical receiver system;

FIG. 3 illustrates another example optical receiver system;

FIG. 4 depicts an example system including a plurality of opticalfront-ends;

FIG. 5 illustrates an example optoelectronic module including at leastone optical receiver;

FIG. 6 illustrates an example implementation of a directional coupler ofthe optical receiver systems of FIGS. 2A-3;

FIG. 7 depicts plots of simulated results of the directional coupler ofFIG. 6;

FIG. 8 is an overhead view of an example SiN—Si multimode adiabaticcoupler; and

FIG. 9 illustrates an example optical system in which the SiN—Simultimode adiabatic coupler of FIG. 8 may be implemented,

all arranged in accordance with at least one embodiment describedherein.

DETAILED DESCRIPTION OF SOME EXAMPLE EMBODIMENTS

Various embodiments disclosed herein relate to optical receivers. Morespecifically, some embodiments relate to optical receivers including aplurality of signal paths, which may be selectable based on a detectedoutput power level of at least one of the signal paths.

Optical transceivers may include a receiver optical subassembly (“ROSA”)and a transmitter optical subassembly (“TOSA”). The ROSA may include aphotodiode or other optical detector for detecting optical signals andsensing circuitry for converting the optical signals to electricalsignals compatible with other network components. The TOSA may include alaser or other suitable light source for transmitting optical signalsand may further include control circuitry for modulating the laseraccording to an input digital data signal and a photodetector to monitorlaser power.

Conventional optical receivers that use vertically illuminatedphotodetectors and published silicon photonics receivers that usewaveguide photodetectors may use one photodetector/transimpedanceamplifier (TIA) combination to cover a relatively large input opticalpower dynamic range. To prevent receiver overload at high optical power,a transimpedance circuit may include shunt elements at an input of theTIA, a reduced input stage gain, and/or signal clamping circuits thatmay complicate the design and compromise the sensitivity and linearityof a TIA input stage.

Silicon photonics or other integrated photonic technologies may enableuse of multiple integrated photodetectors and the ability to split anincoming signal into multiple signal paths. Directional couplers mayoffer extremely low optical insertion loss and controlled splittingratios, which, when combined with the integrated photodetectors, enablenew circuit topologies that may circumvent the limitations found inconventional optical receivers.

Embodiments of the present disclosure will be explained with referenceto the accompanying drawings.

FIG. 1 illustrates an example optical receiver system 100 (hereinafter“system 100”), arranged in accordance with at least one embodimentdescribed. The system 100, which may include, for example, an opticalreceiver, includes an optical fiber 102, a spot size converter 104, anda photonic integrated circuit (PIC) 106. The optical fiber 102 mayinclude any type of optical fiber, such as a multi-mode fiber orsingle-mode fiber, configured to transmit an optical signal. During acontemplated operation of the system 100, an optical signal may betransmitted to the photonic IC 106 via the optical fiber 102.

FIG. 2A depicts an example optical receiver system 200A (hereinaftersystem 200A), arranged in accordance with at least one embodimentdescribed herein. The system 200A may include, correspond to, or beincluded in the system 100 of FIG. 1. The system 200A, which includes anoptical receiver, includes the optical fiber 102 and the spot sizeconverter 104 of FIG. 1. The system 200A further includes a directionalcoupler 206 and multiple signal paths. For example, in this example, thesystem 200A includes signal paths 207A and 207B, collectivelyhereinafter “signal paths 207”. The signal path 207A includes aphotodetector 208A, a TIA 210A, and an interpolator 212. The signal path207B includes a photodetector 208B, a TIA 210B, and an interpolator 212.The TIAs 210A, 210B may be collectively referred to hereinafter as “TIAs210”. The path 207B further includes a waveguide terminator 209.

Each of photodetectors 208A and 208B (collectively “photodetectors 208”)may be configured to generate a current in response to an incidentoptical signal. The optical power of the incident optical signal maydetermine the current that flows in the corresponding one of thephotodetectors 208. In effect, the optical signal may generate a currentin the photodetectors 208 that corresponds to a digital data carried viathe optical fiber 102. According to some embodiments, the TIA 210A andTIA 210B may be similar, or identical, circuits, and may be configuredfor optimal input referred noise performance.

As described more fully below, the system 200A may be configured toenable one signal path (e.g., either the signal path 207A or 207B) andto disable the other signal path based on an output power level withinthe system 200A (e.g., within one of the signal paths 207).

As depicted, the interpolator (also referred to herein as “adder”) 212is coupled to an output of each of the TIA 210A and the TIA 210B.Further, the system 200A includes an amplifier 214 coupled to an outputof the interpolator 212, and an optical power sensing circuit 216, whichmay be coupled to the TIA 210A, the TIA 210B, the interpolator 212,and/or the amplifier 214. The optical power sensing circuit 216 may beconfigured to detect an optical power level within the system 200A. Morespecifically, the optical power sensing circuit 216 may detect theoptical power level within, for example, the TIA 210A, the TIA 210B, atan output of the interpolator 212, and/or at an output of the amplifier214. Further, as described more fully below, based on the detectedoptical power level, the system 200A may transition between the signalpaths 207 (e.g., from the signal path 207A to the signal path 207B, orvice versa). The optical power sensing circuit 216 may also be referredto as and/or may include an optical power sensor.

In some embodiments, the photonic IC 106 (see FIG. 1) may include and/ormay have coupled thereto the directional coupler 206, the photodetectors208, the TIA 210A, the TIA 210B, the interpolator 212, the amplifier214, and/or the optical power sensing circuit 216 of FIG. 2A.

During a contemplated operation of the system 200A, an optical signalmay be received at the directional coupler 206, and the directionalcoupler 206 may split the received optical signal into two portions,each directed to a different one of the signals paths 207. In someembodiments, one signal path, such as the signal path 207A, may beconfigured to convey a certain portion (e.g., a percentage) of theoptical signal and another signal path, such as the signal path 207B,may be configured to convey another portion (e.g., another percentage,such as a lesser percentage) of the optical signal. More specifically,for example, the signal path 207A may be configured to convey X % of theoptical signal while the signal path 207B may be configured to convey100−X % of the signal. For example, X may be a value betweensubstantially 75 and substantially 100. Thus, as one example, the signalpath 207A may convey 75% of the optical signal and the signal path 207Bmay convey 25% of the optical signal. In another example, the signalpath 207A may convey 80% of the optical signal and the signal path 207Bmay convey 20% of the optical signal. In yet another example, the signalpath 207A may convey 90% of the optical signal and the signal path 207Bmay convey 10% of the optical signal.

Although the system 200A is illustrated in FIG. 2A as including twosignal paths 207, the present disclosure is not so limited. Moregenerally, the system 200A may include multiple signal paths (e.g., twosignal paths, three signal paths, four signal paths, five signal paths,etc.)

Moreover, in response to an incident optical signal thereon, each of thephotodetectors 208 may generate an associated electrical signal, such asa current signal, which may be conveyed to an associated one of the TIAs210. More specifically, the photodetector 208A may convey a currentsignal to the TIA 210A and the photodetector 208B may convey a currentsignal to the TIA 210B.

Further, in some embodiments, one of the TIA 210A and the TIA 210B maybe enabled and the other of the TIA 210A and the TIA 210 may bedisabled. More specifically, in some embodiments, the signal path 207A,and more specifically the TIA 210A, may be configured to be enabled(e.g., in an active mode) at low optical power, and the signal path207B, and more specifically the TIA 210B, may be configured to bedisabled (e.g., in a non-active mode) (e.g., at the same low opticalpower). At an increased or high optical power in the system 200A, anoutput signal out of the TIA 210A may be distorted while an outputsignal out of the TIA 210B, which may be a fraction of the output signalof the TIA 210A (e.g., ((100−X)/X)), may be linear. Accordingly, in someembodiments, the signal path 207A, and more specifically the TIA 210A,may be configured to be disabled (e.g., non-active) at high opticalpower, and the TIA 210B may be configured to be enabled (e.g., active)at high optical power since the TIA 210B receives only a fraction of theoptical power and thus generates a non-distorted signal at its outputeven when the optical power of the optical signal received by the system200A is a high optical power.

The optical power sensing circuit 216 may be configured to detect theoptical power level in the system 200A based on, e.g., the output of theTIA 210A, the output of the TIA 210B, the output of theinterpolator/adder 212, and/or the output of the amplifier 214.Alternatively or additionally, the optical power sensing circuit 216 maycontrol switchovers between the TIA 210A and the TIA 210B depending onthe detected optical power. For example, if the detected optical powerincreases from low optical power to high optical power, e.g., if thedetected optical power increases above a threshold optical power, theoptical power sensing circuit 216 may disable the TIA 210A and enablethe TIA 210B. Alternatively or additionally, if the detected opticalpower decreases from high optical power to low optical power, e.g., ifthe detected optical power decreases below the threshold optical power,the optical power sensing circuit 216 may enable the TIA 210A anddisable the TIA 210B. Alternatively or additionally, there may be atransitional input optical power range (described below) defined betweena first threshold optical power and a second threshold optical power; ifthe detected optical power increases from below or above thetransitional input optical power range into the transitional inputoptical power range, the optical power sensing circuit 216 may enableboth of the TIAs 210 until the detected optical power is outside thetransitional input optical power range.

In some embodiments, transitioning from one signal path to anothersignal path may be substantially instantaneous (e.g., only one TIAconveying a signal at any one time). In other embodiments, a transitionperiod may exist wherein more than one path may be active, and one pathmay ramp-up and another path may ramp-down during the transition period(e.g., a time period). Stated another way, a transitional input opticalpower range to activate one signal and deactivate another signal pathmay exist.

The interpolator 212 may select the output of one or both of the TIAs210 to output to the amplifier 214, e.g., based on a control signal fromthe optical power sensing circuit. Alternatively or additionally, theinterpolator 212 may combine, e.g., add, the output of the TIA 210A andthe output of the TIA 210B to output to the amplifier 214. For example,if both TIAs 210 are enabled, e.g., during a transition period where thedetected optical power is in the transitional input optical power range,a control signal from the optical power sensing circuit 216 may causethe interpolator 212 to add the outputs of the TIAs 210 to output thecombined output to the amplifier 214.

The amplifier 214 may be configured to amplify the output of theinterpolator 212 to be at or near a target output level and/or within atarget output level range of the system 200A. The amplifier 214 mayinclude an amplifier or an attenuator with a fixed or variable gain,such as a variable gain amplifier (VGA), with or without automatic gaincontrol. In these and other embodiments, the output of the interpolator212 may have a signal amplitude proportional to the signal at the outputof the TIA 210A until it reaches a crossover region (or transitionalinput optical power range of the system 200A), at which point theamplitude at the output of the interpolator 212 may remain constantuntil the first signal path 207A is no longer active. Then, the outputof the interpolator 212 may have a signal amplitude proportional to thesignal at the output of the second TIA 210B. Thus, the foregoingarrangement may increase dynamic range without necessarily ensuringlinearity at the output of the interpolator 212. The amplifier 214 mayinclude internal automatic gain control (see, e.g., FIG. 4) to providelinearity.

By transitioning from one signal path to another signal path, thedynamic range of system 200A may be improved (e.g., by X/(100−X)). Forexample, if X=80%, the optical dynamic range may be increased by80/20=4=6 dB. In this example, the sensitivity of the system 200A may bedegraded by, for example, 10.LOG 10 (0.8)=1 dB. Therefore, the dynamicrange of the system 200A may improve by, for example, 5 dB (e.g.,6−1=5), when compared to only a single path (e.g., the signal path 210A)with X=100%.

In some embodiments, the directional coupler 206 may include apolarization dependent directional coupler 206. In other embodiments,the directional coupler 206 may include a polarization independentdirectional coupler 206. An example polarization independent directionalcoupler is described in more detail elsewhere herein.

FIG. 2B depicts another example optical receiver system 200B(hereinafter “system 200B”), arranged in accordance with at least oneembodiment described herein. The system 200B may include, correspond to,or be included in the system 100 of FIG. 1. The system 200B of FIG. 2Bmay include the same or similar components as the system 200A of FIG.2A, including the directional coupler 206, the signal paths 207, thephotodetectors 208, the TIAs 210, the interpolator 212, the amplifier214, and the optical power sensing circuit 216. Accordingly, the system200B may generally function in the same or similar manner as the system200A, and a description of the foregoing components and the operation ofthe system 200B will not be repeated.

In addition, the system 200B of FIG. 2B includes two silicon nitride(SiN)-silicon (Si) couplers 204A, 204B (collectively hereinafter “SiN—Sicouplers 204”), including one in each of the signal paths 207. Inparticular, the SiN—Si coupler 204A may be included in the signal path207A to couple one output of the directional coupler 206 to thephotodetector 208A of the signal path 207A, while the SiN—Si coupler204B may be included in the signal path 207B to couple another output ofthe directional coupler 206 to the photodetector 208B of the signal path207B. An example implementation of the SiN—Si couplers 204 is describedelsewhere.

FIG. 3 depicts another example optical receiver system 300 (hereinafter“system 300”), arranged in accordance with at least one embodimentdescribed herein. The system 300 may include, correspond to, or beincluded in the system 100 of FIG. 1. In some embodiments, the system300 may be implemented with silicon photonics technology devices. Thesystem 300, which may include an optical receiver, includes the opticalfiber 102 and an interface 303, which may include, for example, agrating coupler, a spot size coupler, and/or a polarization splitter.The system 300 further includes directional couplers 306A and 306B(collectively “directional couplers 306”). Further, in this embodiment,the system 300 includes multiple signal paths 307A and 307B(collectively “signal paths 307”). The signal path 307A includes aphotodetector 308A, the TIA 210A and the interpolator 212. The signalpath 307B includes a photodetector 308B, the TIA 210B, and theinterpolator 212. The photodetectors 308A, 308B may be collectivelyreferred to as “photodetectors 308”) In some embodiments in which theinterface 303 includes a polarization splitter, transverse electric (TE)waves of the received optical signal may be transmitted to one of thedirectional couplers 306 and transverse magnetic (TM) waves of thereceived optical signal may be transmitted to the other one of thedirectional couplers 306.

The interpolator 212, the amplifier 214, and/or the optical powersensing circuit 216 may operate within the system 300 in a similar oridentical manner as in the system 200A and as already described above.

Each of photodetectors 308 may be configured to generate a current inresponse to an incident optical signal. The optical power of theincident optical signal may determine the current that flows in each ofthe photodetectors 308. In effect, the optical signal may generate acurrent in the photodetectors 308 that corresponds to a digital datacarried via the optical fiber 102.

The system 300 further includes the interpolator 212 coupled to anoutput of each of the TIA 210A and TIA 210B, the amplifier 214 coupledto an output of the interpolator 212, and the optical power sensingcircuit 216, which may be coupled to the TIAs 210, the interpolator 212,and/or the amplifier 214.

In some embodiments, the photonic IC 106 (see FIG. 1) may include and/ormay have coupled thereto the directional couplers 306, thephotodetectors 308, the TIAs 210, the interpolator 212, the amplifier214, and/or the optical power sensing circuit 216 of FIG. 3.

Similar to the system 200A of FIG. 2A, during a contemplated operationof the system 300, an optical signal propagating on the optical fiber102 is received at the interface 303 and may be divided into a firstcomponent with a first polarization (e.g., TE polarization) and a secondcomponent with a second polarization (e.g., TM polarization). One of thepolarization c, components may be directed to the directional coupler306A and the other of the polarization components may be directed to theother directional coupler 306B.

The directional coupler 306A may split a received optical signal, suchas one of the polarization components received from the interface 303,into two portions, each directed to a different one of the signal paths307. Similarly, the directional coupler 306B may split a receivedoptical signal, such as the other one of the polarization componentsreceived from the interface 303, into two portions, each directed to adifferent one of the signal paths 307. In some embodiments, one path,such as path 307A, may be configured to convey a certain portion (e.g.,a percentage) of a received optical signal and another signal path, suchas the signal path 307B, may be configured to convey another portion(e.g., another percentage, such as a lesser percentage) of the receivedoptical signal. More specifically, for example, the signal path 307A maybe configured to convey X % of the received optical signal (whether fromeither or both of the directional couplers 306) while the signal path307B may be configured to convey 100−X % of the received optical signal(whether from either or both of the directional couplers 306). Forexample, X may be a value between substantially 75 and substantially100. Thus, as one example, the signal path 307A may convey 75% of thereceived optical signal and the signal path 307B may convey 25% of thesignal. In another example, the signal path 307A may convey 80% of thereceived optical signal and the signal path 307B may convey 20% of thereceived optical signal. In yet another example, the signal path 307Amay convey 90% of the received optical signal and the signal path 307Bmay convey 10% of the received optical signal.

Although the system 300 is illustrated in FIG. 3 as including two signalpaths 307, the present disclosure is not so limited. More generally, thesystem 300 may include multiple signal paths (e.g., two signal paths,three signal paths, four signal paths, five signal paths, etc.)

Moreover, in response to an incident optical signal thereon, each ofphotodetectors 308 may generate an associated electrical signal, such ascurrent signal, which may be conveyed to an associated one of the TIAs210. More specifically, the photodetector 308A may convey a currentsignal to the TIA 210A and the photodetector 308B may convey a currentsignal to the TIA 210B.

Further, in some embodiments, one of the TIA 210A and the 210B may beenabled and the other of the TIA 210A and the TIA 210 may be disabled inthe system 300. More specifically, in some embodiments, the signal path307A, and more specifically the TIA 210A, may be configured to be in anactive mode at low optical power, and the signal path 307B, and morespecifically the TIA 210B, may be configured to be disabled at lowoptical power. Alternatively or additionally, both of the TIAs 210 maybe enabled during a transition period in which the detected opticalpower is within a transitional input optical power range.

At an increased or high optical power in the system 300, an outputsignal out of the TIA 210A may be distorted while an output signal outof the TIA 210B, which may be a fraction of the output signal of the TIA210A, may be linear. Accordingly, in some embodiments, the signal path307A, and more specifically the TIA 210A, may be configured to bedisabled at high optical power, and the TIA 210B may be configured to beactive at high optical power. Accordingly, the dynamic range of thesystem 300 may be improved.

As noted above, in some embodiments, transitioning from one signal pathto another signal path may be substantially instantaneous (e.g., onlyone TIA conveying a signal at any one time). In other embodiments,during a transitional input optical power range, more than one signalpath may be active for a transition period, e.g., one signal path mayramp-up and the other signal path may ramp-down during the transitionperiod (e.g., a time period).

FIG. 4 is a block diagram depicting an example system 400, arranged inaccordance with at least one embodiment described herein. The system 400includes photodetectors 451A, 451B (collectively “photodetectors 451”),receiver front-ends 452A, 452B (collectively “receiver front-ends 452”),the interpolator 212, a control 454, a first VGA 456, a second VGA 458,a buffer 460, and an automatic gain control (AGC) 462. Each of thereceiver front-ends 452 may include at least a portion of the system200A (see FIG. 2A) or at least a portion of the system 300 (see FIG. 3).More specifically, the receiver front-end 452A and/or the receiverfront-end 452B may include the TIA 210A and/or the TIA 210B (see FIGS.2A-3). Alternatively or additionally, the photodetectors 451 may includeor correspond to the photodetectors 208, 308 (see FIGS. 2A-3), while thecontrol 454 may include, may be included in, and/or may correspond tothe optical power sensing circuit 216 of FIGS. 2A-3.

In a contemplated operation, the system 400 may be operated in the sameor a similar manner to one or more of the systems 200A, 200B, 300. Forexample, the control 454 may sense average optical power, e.g., at oneor both of the photodetector 451, and may activate one or both of thereceiver front ends 452 and/or may deactivate one of the receiver frontends 452 depending on the detected optical power. The interpolator 212interpolates output(s) of the receiver front end(s) 452. The output ofthe interpolator 212 may need to be further amplified or attenuated toreach a target output level. The amplification or attenuation may beprovided by one or both VGAs 456, 458, and the amount of amplificationor attenuation may be controlled through an AGC loop that includes theAGC 462. The buffer 460 may provide a drive capability to deliver afinal output of the system 400.

FIG. 5 illustrates an example optoelectronic module 500 (hereinafter“module 500”), arranged in accordance with at least one embodimentdescribed herein. The module 500 may be configured for use intransmitting and receiving optical signals in connection with a hostdevice (not shown). Alternatively or additionally, the module 500 mayinclude a portion or all of one or more of the systems 100, 200A, 300,400 described herein.

As illustrated, the module 500 may include a bottom housing 502, areceive port 504, and a transmit port 506. The module 500 furtherincludes a PCB 508 positioned within the bottom housing 502. The PCB 508may include one or more integrated circuits (e.g., a first integratedcircuit 520 and a second integrated circuit 522) positioned thereon. Inaddition, the module 500 includes a ROSA 510 and a TOSA 512 alsopositioned within bottom housing 502. An edge connector 514 may belocated on an end of the PCB 508 to enable the module 500 toelectrically interface with a host device. As such, the PCB 508 mayfacilitate electrical communication between the host device and the ROSA510 and between the host device and the TOSA 512. Although notillustrated in FIG. 5, the module 500 may additionally include a tophousing that cooperates with the bottom housing 502 to at leastpartially enclose one or more of the other components of the module 500.

The module 500 may be configured for optical signal transmission andreception at a variety of data rates, such as 1 Gb/s, 10 Gb/s, 20 Gb/s,40 Gb/s, 100 Gb/s, or higher, or other data rates. Furthermore, themodule 500 may be configured for optical signal transmission andreception at various distinct wavelengths using wavelength divisionmultiplexing (WDM) using one of various WDM schemes, such as Coarse WDM,Dense WDM, or Light WDM. Furthermore, the module 500 may be configuredto support various communication protocols, such as Fibre Channel andHigh Speed Ethernet. In addition, although illustrated in a particularform factor in FIG. 5, more generally, the module 500 may be configuredin any of a variety of different form factors, such the SmallForm-factor Pluggable (SFP), the enhanced Small Form-factor Pluggable(SFP+), the 10 Gigabit Small Form Factor Pluggable (XFP), the CForm-factor Pluggable (CFP) and the Quad Small Form-factor Pluggable(QSFP) multi-source agreements (MSAs).

The ROSA 510 may house one or more optical receivers (e.g., system 200Aof FIG. 2A and/or system 300 of FIG. 3) that are electrically coupled toan electrical interface 516. The one or more optical receivers may beconfigured to convert optical signals received through the receive port504 into corresponding current electrical signals that are relayed to anintegrated circuit (e.g., within the ROSA 510) (not shown in FIG. 5; seee.g., integrated circuit 106 of FIG. 1) through an electrical interface516 and the PCB 508. The TOSA 512 may house one or more opticaltransmitters, such as lasers, that are electrically coupled to anotherelectrical interface 518. The one or more optical transmitters may beconfigured to convert electrical signals received from a host device byway of the PCB 508 and the electrical interface 518 into correspondingoptical signals that are transmitted through the transmit port 506.

As noted above, an integrated circuit (not shown in FIG. 5), which maybe similar to and/or correspond to the integrated circuit 106 of FIG. 1,may be integrated within the ROSA 510 and may be configured to convertthe current electrical signals to voltage electrical signals and toequalize the voltage electrical signals. The integrated circuit maydrive the equalized voltage electrical signals to a second integratedcircuit (e.g., within the ROSA 510 and/or on the PCB 508), which, insome embodiments, may be a CDR circuit. Thus, in some embodiments, anintegrated circuit, such as the integrated circuit 106 of FIG. 1, may beincorporated into the ROSA 510 and may be used to convert currentelectrical signals to equalized voltage electrical signals.Modifications, additions, or omissions may be made to the module 500without departing from the scope of the present disclosure.

The module 500 illustrated in FIG. 5 is one architecture in whichembodiments of the present disclosure may be employed. This specificarchitecture is only one of countless architectures in which embodimentsmay be employed. The scope of the present disclosure is not intended tobe limited to any particular architecture or environment.

FIG. 6 illustrates an example implementation of the directional coupler206 of FIGS. 2A-3, arranged in accordance with at least one embodimentdescribed herein. The directional coupler 206 of FIGS. 2A-3 may havedifferent implementations than illustrated in FIG. 6, which is providedas one example implementation only.

The directional coupler 206 of FIG. 6 may be an 80/20 polarizationindependent directional coupler implemented in SiN in some embodiments.In more detail, the directional coupler 206 may be configured as pathsor branches formed of SiN waveguides, e.g., SiN cores surrounded on oneor more sides by a cladding. FIG. 6 illustrates the waveguide cores.

The directional coupler 206 may be formed with two SiN waveguides 607Aand 607B (hereinafter collectively “waveguides 607”, or individually“first waveguide 607A” and “second waveguide 607B”) along or at leastcoupled to the signal paths 207A and 207B. The waveguides 607 are formedgenerally to run parallel with each other and then formed with a reducedseparation distance of a gap G of at least a distance 602 to facilitateoptical coupling of the optical signal. Each branch formed by the firstwaveguide 607A and the second waveguide 607B includes an enlarged gapinput section 604, a decreasing gap input section 606 with a slope ofapproximately dy/dx, a minimum gap section 608 (also designated ashaving a length L where the gap G is at a minimum), an increasing gapsection 610 with a slope of approximately dy/dx, and an enlarged gapoutput section 612.

Each of first and second waveguides 607A and 607B are formed to have awaveguide width W illustrated as width 614 and a waveguide thickness T(e.g., in and out of the page in FIG. 6). The width W, thickness T,and/or other dimensions and parameters may refer to dimensions andparameters of the cores of the waveguides 207 unless otherwise noted.For example, the width W 614 may refer to the width of the waveguidecore of each of the waveguides 607. A similar convention may be followedthroughout this document. The SiN material may be formed from a siliconnitride (Si₃N₄) material or other suitable material, e.g., with a highrefractive index of about 1.9 used to determine a coupling length forthe TE and TM polarization modes.

The first waveguide 607A may include an input port 616 and a firstoutput port 618 with the first waveguide 607A being configured with aconsistent width W and thickness T. The second waveguide 607B mayinclude a coupled port 620 and a second output port 622 with the secondwaveguide 607B also being configured with a consistent width W andthickness T. The input port 616 of the first waveguide 607A may beoptically coupled to, e.g., the optical fiber 102 of FIG. 2B through thespot size converter 104. The first output port 618 of the firstwaveguide 607A may be optically coupled to, e.g., the firstphotodetector 208A of FIG. 2B, either directly or through the SiN—Sicoupler 204A of FIG. 2B. The coupled port 620 of the second waveguide607B may be optically coupled to, e.g., the waveguide terminator 209 ofFIG. 2B. The second output port 622 of the second waveguide 607B may beoptically coupled to, e.g., the second photodetector 208B of FIG. 2B,either directly or through the SiN—Si coupler 204B of FIG. 2B.

FIG. 6 further illustrates a table identifying example values forvariously dimensions of the directional coupler 206. Specifically, theidentified dimensions are merely illustrative for an examplemanufacturing process and are not to be considered as limiting. Theexample dimensions in the table for the directional coupler 206 mayresult in an approximately 80%-20% split of the input signal and mayprovide approximately equal distribution of the TE and TM polarizationof the signals in each of the first and second waveguides 607A and 607B.Further, the directional coupler 206 may provide signals to a receiverthat enables the receiver to be configured as a less sophisticatedreceiver (e.g., as discussed with respect to FIGS. 2A and 2B) and allowsfor higher dynamic range and a linear response. Yet further, thedirectional coupler 206 may be polarization independent with nominalinsertion loss with a split ratio tolerance of about 80%+/−5% and20%+1-5% operating at a frequency with a wavelength, for example, ofabout 1310 nanometers (nm) with +1-6.5 nm. The directional coupler 206may be formed using SiN waveguide cores with silicon dioxide (SiO₂)cladding on one or more sides of each of the SiN waveguide cores. Thewaveguide parameters may be as shown in the table of FIG. 6 resulting ina refractive index, for example, of approximately 1.9. Alternatively,the waveguide parameters in the table of FIG. 6 may be modified.

In operation, the input port 616 is configured to receive an opticalsignal including both TE and TM polarization over an operation band offrequencies having wavelengths between, for example, 1.3 μm and 1.32 μm.The optical signal then passes through the first waveguide 607A andcross-couples to the second waveguide 607B in the minimum gap section608 (also designated as to have a length L). Because of the dimensionsidentified herein for the structures forming the directional coupler206, the TE polarization mode and the TM polarization mode of the inputoptical signal are distributed substantially equally in both the firstwaveguide 607A and the second waveguide 607B.

FIG. 7 illustrates simulation plots of results for the directionalcoupler 206 of FIG. 6, arranged in accordance with at least oneembodiment described herein. In FIG. 7, a plot (A) simulates opticalsignal transmission from the first input port 616 to the first outputport 618 (e.g., a ratio of an optical signal present at the first outputport 618 with respect to the optical signal present at the first inputport 616) as a function of optical signal wavelength over a frequencyband having wavelengths between about 1.3 μm to about 1.32 μm. In FIG.7, plot (B) simulates optical signal transmission from the first inputport 616 to the second output port 622 (e.g., a ratio of the opticalsignal present at the second output port 622 with respect to the opticalsignal present at the first input port 616) as a function of opticalsignal wavelength over the frequency band having wavelengths betweenabout 1.3 μm to about 1.32 μm.

In plot (A), the simulated optical signal transmission of the TE mode ofthe optical signal from the first input port 616 to the first outputport 618 is plotted as curve 702 while the simulated optical signaltransmission of the TM mode of the optical signal from the first inputport 616 to the first output port 618 is plotted as curve 704. In plot(B), the simulated optical signal transmission of the TE mode of theoptical signal from the first input port 616 to the second output port622 is plotted as curve 706 while the simulated optical signaltransmission of the TM mode of the optical signal from the first inputport 616 to the second output port 622 is plotted as curve 708.

The curves 702 and 704 of the plot (A) combined with the curves 706 and708 of the plot (B) illustrate a splitting of the input optical signalto about a constant transmission portion of about 0.80 (e.g., 80%) tothe first output port 618 and about 0.20 (e.g., 20%) to the secondoutput port 622 for the frequency band having wavelengths between about1.3 μm to about 1.32 Further, curves 702, 704, 706, and 708 illustrateapproximately equal (less than 0.2%) distributions of TE and TM modesacross the band of interest.

In FIG. 7, a plot (C) illustrates a power plot of the directionalcoupler 206 of FIG. 6. The plot (C) includes a vertical axis on the leftside corresponding to vertical spacing of the directional coupler 206,with the directional coupler 206 in FIG. 7 oriented upside down comparedto the directional coupler 206 illustrated in FIG. 6. The horizontalaxis illustrates distance from the first input port 616, correspondingto a distance of 0 microns, and the first and second output ports 618,622, corresponding to a distance of 41 microns. A vertical legend ofoptical power intensity is also illustrated on the right side of theplot (C). As illustrated, the second output port 622 (illustrated as theupper right-hand branch) exhibits an optical power intensity of about20% when compared to the optical power intensity legend, while the firstoutput port 618 exhibits an optical power intensity of about 80% whencompared to the optical power intensity legend.

Embodiments described herein may alternately or additionally include aSiN—Si multimode adiabatic coupler, which may relax Si tip widthfabrication tolerance. FIG. 8 is an overhead view of an example SiN—Simultimode adiabatic coupler 800 (hereinafter “coupler 800”), arranged inaccordance with at least one embodiment described herein. Either or bothof the SiN—Si couplers 204 of FIG. 2B may be implemented similar oridentical to the coupler 800 of FIG. 8.

The coupler 800 may be included in any of the systems described herein,such as in the systems 200A, 200B of FIGS. 2A, 2B as the SiN—Si coupler204A and/or as the SiN—Si coupler 204B of FIG. 2B. The coupler 800includes a Si waveguide 802 and a SiN waveguide 804. Each of the Siwaveguide 802 and the SiN waveguide 804 includes a core, e.g., a core ofSi for the Si waveguide 802 or a core of SiN for the SiN waveguide 804,and a cladding. FIG. 8 illustrates the cores of the Si and SiNwaveguides 802, 804; the cores of the Si and SiN waveguides 802, 804 andthe cladding are illustrated in FIG. 9 according to an exampleimplementation. The cladding may include SiO₂ or other suitablecladding. In the example of FIG. 8, the SiN waveguide 804 is verticallydisplaced above the Si waveguide 802 and is illustrated assemi-transparent to show the Si waveguide 802 therebeneath. In otherembodiments, the SiN waveguide 804 may be vertically displaced below theSi waveguide 802.

Each of the Si waveguide 802 and the SiN waveguide 804 includes atapered section at an end thereof. In particular, the Si waveguide 802includes a Si taper 806 and the SiN waveguide 804 includes a SiN taper808. An end of the Si waveguide 802 opposite the Si taper 806 may beoptically coupled to an optical receiver, such as a germanium (Ge)detector. For example, the photodetector 208A of FIG. 2B may include aGe detector to which the end of the Si waveguide 802 opposite the Sitaper 806 may be coupled.

The coupler 800 may be configured to adiabatically couple light from theSiN waveguide 804 through the SiN taper 808 and the Si taper 806 intothe Si waveguide 802, which light may then be coupled out to the Gedetector or other optical receiver. Additional details regardingadiabatic coupling are disclosed in U.S. Pat. No. 9,405,066, issued onAug. 2, 2016 (hereinafter the '066 patent) and U.S. application Ser. No.15/596,958 (hereinafter the '958 application), filed May 16, 2017. The'066 patent and the '958 application are incorporated herein byreference in their entireties.

From left to right in FIG. 8, the Si taper 806 may gradually change froma relatively narrow tip to a multimodal waveguide with a width w_(Si)suitable for multimode optical signals. In an example implementation,the width of the relatively narrow tip of the Si taper 806 may be in arange from 100-120 nm and the width w_(Si) may be about 1 micrometer(μm). A length of the Si taper 806 is denoted in FIG. 8 as L_(Si taper).Above the Si taper 806, the SiN waveguide 804 may have a constant widthand/or height, e.g., the portion of the SiN waveguide 804 above the Sitaper 806 does not taper.

Also from left to right in FIG. 8, the SiN taper 808 may taper down froma width w_(SiN) suitable for multimode optical signals to a relativelynarrow tip. In an example implementation, the width w_(SiN) may be about1 μm and the width of the relatively narrow tip of the SiN taper 808 maybe around 250 nm. Although the widths w_(Si) and w_(SiN) are equivalentin this example, in other embodiments they may be different. A length ofthe SiN taper 808 is denoted in FIG. 8 as L_(SiN taper), and may beabout 0.01 mm in some embodiments. Below the SiN taper 808, the Siwaveguide 802 may have a constant width and/or height, e.g., the portionof the Si waveguide 802 below the SiN taper 808 does not taper. An endof the SiN waveguide 804 opposite the SiN taper 808 may be coupled to,e.g., an output of the directional coupler 206 of FIG. 2B, such as thefirst output port 618 or the second output port 622 of the directionalcoupler 206 of FIG. 6.

FIG. 9 illustrates an example optical system 900 in which the coupler800 of FIG. 8 may be implemented, arranged in accordance with at leastone embodiment described herein. The optical system 900 may include a Sisubstrate 902, a buried oxide (BOX) layer 904 formed on the Si substrate902, a Si waveguide layer 906 formed on the BOX layer 904 and thatincludes one or more Si waveguides such as the Si waveguide 802 of FIG.8, a SiN slab 910A formed on the Si waveguide layer 906, a SiN waveguidelayer 912 formed on the SiN slab 910A and that includes one or more SiNwaveguides such as the SiN waveguide 804 of FIG. 8, and one or moredielectric layers 918 formed on the SiN waveguide layer 912. Optionally,a second SiN slab 910B may be formed between the SiN waveguide layer 912and the dielectric layers 918. Each of the Si waveguide layer 906 andthe SiN waveguide layer 912 may additionally include dielectricmaterial, such as SiO₂ and/or other material(s) that serves as acladding for the Si waveguide(s) and SiN waveguide(s) in each respectiveSi or SiN waveguide layer 906, 912.

The '066 patent and the '958 application disclose various exampledetails of the elements included in the optical system 900 as well asvarious alternative arrangements (e.g., different order of layers)and/or other embodiments. The principles disclosed herein may beimplemented in combination with none or one or more of the details,alternative arrangements, and/or other embodiments of the '066 patentand/or the '958 application.

As illustrated in FIG. 9, the Si waveguide 802 may include a heighth_(Si) and the width w_(Si). The SiN waveguide 804 may include a heighth_(SiN) and the width w_(SiN). FIG. 9 is a cross-sectional view of theoptical system 900 taken at the location at which the width w_(Si) ofthe Si waveguide 802 equals the width w_(SiN) of the SiN waveguide 804.Stated another way, and with combined reference to FIGS. 8 and 9, thecross-sectional view of the optical system 900 may be taken at alocation aligned to both the rightmost end in FIG. 8 of the Si taper 806and to the leftmost end in FIG. 8 of the SiN taper 808.

The height h_(Si) of the Si waveguide 802 may be about 300 nm or someother value in an example implementation. Alternatively or additionally,the width w_(Si) of the Si waveguide 802 may be about 100 nm to 1,000 nm(or 0.1 μm to 1 μm) depending on which part of the Si waveguide 802 isbeing measured. For instance, the tip of the core of the Si waveguide802 may be about 100 nm up to 120 nm which then tapers gradually up to 1μm.

The height h_(SiN) of the SiN waveguide 804 may be about 600 nm or someother value in an example implementation. Alternatively or additionally,the width w_(SiN) of the SiN waveguide 804 may be about 250 nm to 1 μmdepending on which part of the SiN waveguide 804 is being measured. Forinstance, the tip of the core of the SiN waveguide 804 may be about 250nm which then tapers gradually up to 1 μm. In other embodiments, thewidth and/or height w_(Si), w_(SiN), and/or h_(SiN) of the Si and SiNwaveguides 802 and 804 may be different than the foregoing values.

Additional details regarding the coupler 800 and/or variations thereofare disclosed in the '958 application.

Terms used in the present disclosure and especially in the appendedclaims (e.g., bodies of the appended claims) are generally intended as“open” terms (e.g., the term “including” should be interpreted as“including, but not limited to,” the term “having” should be interpretedas “having at least,” the term “includes” should be interpreted as“includes, but is not limited to,” etc.).

Additionally, if a specific number of an introduced claim recitation isintended, such an intent will be explicitly recited in the claim, and inthe absence of such recitation no such intent is present. For example,as an aid to understanding, the following appended claims may containusage of the introductory phrases “at least one” and “one or more” tointroduce claim recitations. However, the use of such phrases should notbe construed to imply that the introduction of a claim recitation by theindefinite articles “a” or “an” limits any particular claim containingsuch introduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should be interpreted to mean “at least one”or “one or more”); the same holds true for the use of definite articlesused to introduce claim recitations.

In addition, even if a specific number of an introduced claim recitationis explicitly recited, those skilled in the art will recognize that suchrecitation should be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, means at least two recitations, or two or more recitations).Furthermore, in those instances where a convention analogous to “atleast one of A, B, and C, etc.” or “one or more of A, B, and C, etc.” isused, in general such a construction is intended to include A alone, Balone, C alone, A and B c, together, A and C together, B and C together,or A, B, and C together, etc.

Further, any disjunctive word or phrase presenting two or morealternative terms, whether in the description, claims, or drawings,should be understood to contemplate the possibilities of including oneof the terms, either of the terms, or both terms. For example, thephrase “A or B” should be understood to include the possibilities of “A”or “B” or “A and B.”

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A system, comprising: an optical receiverincluding: a directional coupler configured to receive an optical signaland split the optical signal into a first signal including a firstportion of the optical signal and a second signal including a secondportion of the optical signal; a first signal path configured to receivethe first signal and including: a first photodetector; a firsttransimpedance amplifier (TIA) coupled to the first photodetector; andan interpolator coupled to the first TIA; a second signal pathconfigured to receive the second signal and including: a secondphotodetector; a second TIA coupled to the second photodetector; and theinterpolator coupled to the second TIA, the interpolator configured togenerate an output signal based on at least one of an output of thefirst TIA and an output of the second TIA; and an optical power sensingcircuit configured to detect a power level of at least one of a signalwithin the first signal path, a signal within the second signal path, orthe output signal from the interpolator; wherein the optical receiver isconfigured to select at least one of the first signal path or the secondsignal path to generate the output signal based on the detected powerlevel.
 2. The system of claim 1, further comprising an amplifier coupledto an output of the interpolator and configured to generate an amplifiedoutput signal based on the output signal.
 3. The system of claim 1,wherein the directional coupler comprises a silicon nitride (SiN)polarization independent directional coupler.
 4. The system of claim 3,wherein the SiN polarization independent directional coupler comprises:a first SiN waveguide including an optical input port to receive theoptical signal and a first output port optically coupled to the firstphotodetector in the first signal path; and a second SiN waveguideincluding a terminated port and a second output port optically coupledto the second photodetector in the second signal path, wherein: thefirst and second SiN waveguides are spaced apart to inhibit opticalcoupling in a first region; the first and second SiN waveguides aredecreasingly spaced apart with respective slopes of the first and secondSiN waveguides in a second region; the first and second SiN waveguidesare substantially parallel for a distance L and spaced apart with anoptical coupling gap G in a third region; the first and second SiNwaveguides are increasingly spaced apart with respective slopes of thefirst and second SiN waveguides in a fourth region; and the first andsecond SiN waveguides are spaced apart to inhibit optical coupling in afifth region.
 5. The system of claim 1, wherein the first signalincluding the first portion of the optical signal comprises between 75%and 90% of the optical signal.
 6. The system of claim 1, furthercomprising at least one of a grating coupler, a spot size converter, anda polarization splitter coupled between an optical fiber and thedirectional coupler.
 7. The system of claim 1, wherein: the first signalpath further includes a first silicon nitride (SiN)-silicon (Si)multimode adiabatic coupler between a first output port of thedirectional coupler and the first photodetector of the first signalpath; and the second signal path further includes a second SiN—Simultimode adiabatic coupler between a second output port of thedirectional coupler and the second photodetector of the second signalpath.
 8. The system of claim 7, further comprising: a Si substrate; aburied oxide (BOX) layer formed above the Si substrate; a Si waveguidelayer formed above the BOX layer; and a silicon nitride (SiN) waveguidelayer formed above the Si waveguide layer, wherein: the directionalcoupler is formed in the SiN waveguide layer; each of the first andsecond SiN—Si multimode adiabatic couplers is formed in the Si waveguidelayer and the SiN waveguide layer and includes: a multimode Si waveguideformed in the Si waveguide layer, the Si waveguide including a Si taper;and a SiN waveguide formed in the SiN waveguide layer, the SiN waveguideincluding a SiN taper aligned in two orthogonal directions with aportion of the multimode Si waveguide that is continuous with andexcludes the Si taper, the Si taper being aligned in two orthogonaldirections with a portion of the SiN waveguide that is continuous withand excludes the SiN taper.
 9. An optical receiver, comprising: at leastone directional coupler having at least one input configured to coupleto an optical fiber; a first signal path including a first photodetectorcoupled to an output of the at least one directional coupler, a firsttransimpedance amplifier (TIA) including an input coupled to the firstphotodetector, and an adder coupled to an output of the first TIA; asecond signal path including a second photodetector coupled to an outputof the at least one directional coupler, a second TIA including an inputcoupled to the second photodetector, and the adder coupled to an outputof the second TIA; and an optical power sensing circuit coupled to atleast one of the first TIA, the second TIA, the adder, and an output ofthe optical receiver.
 10. The optical receiver of claim 9, wherein theoptical power sensing circuit is configured to detect at least one of asignal power level within the first signal path, a signal power levelwithin the second signal path, a signal power level at the adder, or asignal power level at the output of the optical receiver.
 11. Theoptical receiver of claim 10, wherein the optical receiver is configuredto: enable the first signal path and disable the second signal path whenthe signal power level is equal to or less than a threshold value; anddisable the first signal path and enable the second signal path when thesignal power level is greater than the threshold value.
 12. The opticalreceiver of claim 10, wherein the optical receiver is configured to:enable the first signal path and disable the second signal path when thesignal power level is less than a first threshold value; disable thefirst signal path and enable the second signal path when the signalpower level is greater than a second threshold value that is greaterthan the first threshold value; and at least partially enable each ofthe first signal path and the second signal path when the signal powerlevel is between the first threshold value and the second thresholdvalue.
 13. The optical receiver of claim 9, wherein the first signalpath is configured to receive a first percentage of an input signal andthe second signal path is configured to receive a second, differentpercentage of the input signal, wherein the first percentage comprises Xpercent of the input signal and the second, different percentagecomprises 100−X percent of the input signal.
 14. The optical receiver ofclaim 9, further comprising at least one of a grating coupler, a spotsize converter, and a polarization splitter coupled to an input of theat least one directional coupler.
 15. The optical receiver of claim 9,wherein: the directional coupler comprises an 80/20 silicon nitride(SiN) polarization independent directional coupler; the optical receiverfurther comprises a first SiN-silicon (Si) multimode adiabatic couplerthat optically couples a first output port of the 80/20 SiN polarizationindependent directional coupler to the first photodetector of the firstsignal path; and the optical receiver further comprises a second SiN—Simultimode adiabatic coupler that optically couples a second output portof the 80/20 SiN polarization independent directional coupler to thesecond photodetector of the second signal path.
 16. A method,comprising: splitting an optical signal into a first optical signal anda second optical signal via a directional coupler, the first opticalsignal including a first portion of the optical signal and the secondoptical signal including a second, lesser portion of the optical signal;converting the first optical signal into a first current signal in afirst signal path; converting the second optical signal into a secondcurrent signal in a second signal path; amplifying the first currentsignal to generate a first amplified signal in the first signal path;directly or indirectly detecting a power level of the optical signal;and disabling the first signal path and enabling the second signal pathin response to the power level of the optical signal increasing above athreshold value.
 17. The method of claim 16, further comprisingreceiving the optical signal at the directional coupler from an opticalfiber.
 18. The method of claim 16, wherein directly or indirectlydetecting the power level of the optical signal comprises directlydetecting average photodiode current in at least one of: a firstphotodetector that converts the first optical signal into the firstcurrent signal; a first transimpedance amplifier (TIA) coupled toreceive the first current signal from the first photodetector; a secondphotodetector that converts the second optical signal into the secondcurrent signal; and a second TIA coupled to receive the second currentsignal from the second photodetector.
 19. The method of claim 16,wherein directly or indirectly detecting the power level of the opticalsignal comprises indirectly detecting the power level of the opticalsignal by detecting amplitude or power of an electrical signal at anoutput of an interpolator/adder coupled to both the first signal pathand the second signal path.
 20. The method of claim 16, whereindisabling the first signal path and enabling the second signal pathcomprises disabling a first transimpedance amplifier (TIA) in the firstsignal path and enabling a second TIA in the second signal path.